The present disclosure relates generally to the machining of composite material. In particular, this disclosure relates to machining of holes in composite material.
Composite components are being utilized in a wide variety of articles of manufacture due to their high strength and light weight. This is particularly true in the field of aircraft manufacturing. Typical materials used in the manufacture of composite components include glass or graphite fibers that are embedded in resins, such as phenolic, epoxy, and bismaleimide resins. A composite lamination can be built up by laying successive plies of fiber tows (e.g., carbon fiber tows preimpregnated with a thermoset epoxy resin) around a mandrel and then curing. As more advanced materials and a wider variety of material forms have become available, aerospace usage of composites has increased.
Certain machining applications require drilling and/or reaming a hybrid stack-up of materials. A hybrid stack-up of materials may be defined as layers of discontinuous materials such as a carbon fiber-reinforced plastic (CFRP) composite material and titanium, aluminum or steel. For example, certain aircraft require a wing made from a composite material, such as CFRP, be joined to a titanium section of an aircraft body with fasteners that pass through holes made through the mating sections. When using fasteners to attach composite skins to metal substrates, coaxial holes must be drilled in both the skin and an underlying metal substrate. High-quality holes must be produced in such materials with dimensions within narrow tolerances. The wing-to-body join task typically requires a three-step conventional drilling process comprising a pilot drill, followed by a step drill, followed by a finish diameter reamer.
Reamers are cutting tools that are typically used to perform the final cutting operation on holes, particularly holes with small tolerances. Specifically, reamers perform secondary cutting operations after a hole has been drilled close to a desired final size. Reamers therefore typically have an external diameter that is slightly larger than that of the drilled hole, and are designed to finish the hole to within a small tolerance of the desired size and to provide a relatively smooth inner wall.
Standard reamers typically include a shank, a body portion at one end of the shank, and a plurality of teeth, such as 4-8 teeth, that are spaced around the body portion and extend outwardly therefrom to form the cutting surfaces of the reamer. Each tooth includes a rake face and a cutting edge that actually engages the workpiece in the course of reaming a hole. In some cases, the teeth are uniformly spaced around the body portion. In other cases, the teeth have non-uniform or irregular spacing.
During the machining of holes in composite material, severe delamination can occur if a reaming operation is performed prior to a hole being drilled or after a hole has been only partially drilled. The repairs for this kind of damage are very expensive and production flow must be halted until the problem is resolved.
Mechanics use visual inspection and tooling pins to assure that the pre-hole is complete before they move on to the reaming operation. Visual inspection of these holes is difficult in some areas due to limited access and time consuming.
Thus there is a need for a system to inhibit or terminate (without human intervention) the performance of a reaming operation if the pre-hole is missing or other dimensional characteristics do not meet the pre-hole requirements such as depth, diameter, orientation, and location.